Radio receiving apparatus



Sept. 6, 1932. v H. A. WHEELER 1,875,837

RADIO RECEIVING APPARATUS Filed Jul 7, 1951 INVENTOR HAROLD 4. WHL-ELERMw W ATTORNEYS Patented Sept. 6, 1932 t 1,875,837

UNITED STATES PATENT OFFICE HAROLD A. WHEELER, OF GREAT NECK, NEW YORK,ASSIGNOR TO HAZEL' IINE CORPORATION RADIO RECEIVING APPARATUSApplication filed July 7, '1931. Serial .No. -549,149.

The present invention relates to the seleccurrent with a consequent lossof the signal tion of a radio-frequency signal being transenergy. mittedon one carrier frequency and the It is therefore another ob ect of thepressimultaneous reduction of interference being ent invention toprovide an improvedradio transmitted on other frequencies not greatlyreceiving apparatus in which the attenuation different from thefrequency of the desired of the image frequency obtainable by ign l,means of the tapped coil just described may The invention isparticularly applicable to be had, and yet one in which there will be noa superheterodyne type of receiver. It is ultimate loss in amplificationor gain incident 10 Well known that the superheterodyne is sensito therejector action. tive to signals of two frequencies when set to Theseand further objects will be apparent receive any given frequency. Thetwo fre- 1n connection with the following description quencies differfrom each other by twice the when considered in connection with thedrawamount of the off-set or intermediate freing. 5 quency to which theintermediate-frequency In accomplishing the objects of theinvenamplifier is permanently tuned. tion, a signal selecting system isprovided It is a common practice to employ a signal comprising an inputtransformer having a' selecting system to amplifygthe desired fretunedsecondary, the tuning of which may be quency of the two carrierfrequencies to which varied to cause the tuned circuit to respond 30 thesuperheterodyne receiver responds, the to frequencies covering thebroadcast band, desired frequency herein being called the sigforinstance. The secondary of said transnal frequency, and which s gnalselecting sysformer is tapped at such a point that the tem attenuatesthe undesired Carrier unused portion of the transformer together quencyor disturbance occurring atthe other with the tuning condenser willconstitute a frequency, herein called the image freby-pass to currentsof the 'mage frequency. quency. In other words, the termi als'of thetapped I The relativeattenuation of the image file inductance will be atnode potential relative quency can be increased by simultaneously tothe. signal frequency. The tapped portion tuning several selectivecircuits to the signal of th in ut inductance is connected with a 30frequency. H W V I, if th i n H second tuned circuit comprising aninducmitting at the image frequency comes in tance and capacitance, bymeans of a link cirrather strong, it is difficult to differentiate beit,hi h i lud a, portion of thecapacitween the signal and image,frequencietive reactance of-the second tuned circuit. It is the object of thepresent inventi n to A capacity may also be included in the link 35 Q?this d1sadvantage 111 P circuit for the purpose of causing it toreheterodyne r v spond to a current of a definite frequency, Toaccomplish this object it. is proposed to as may be desired. The.inductance of the attenuate the undesired image frequency by d t d i itmay b t d i a i ithe use of a special rejector circuit comprising 1 annr to provid for further image 40- an input transformer of which thesecondary frequency reduction. is tapped to constitute the connection tothe H i thu briefly described the inveninput of the radio-frequencyamplifier or of tion,attention isinvited tothe accompanying the firstdetector in a manner similar to that drawing which shows a selectivecircuit em- I disclosed in U. S. Patent No. 1,680,424, issued bodyingthe present invention. August 14', 1928, to W lliam A. MacDonald. Theantenna or input circuit comprises The tap is so selected that theterminals of antenna 1, ground terminal 2, and the prithe portion of thesecondary coil are at node mary coil 3. The first tuned circuitcomprises potential relative to currentspf the image secondary coil. 4and} variable tuning confrequency. However, such a system results denser5, the secondary coil {1 being coupled in the by-passing of a portion ofthe signal to the primary coil 3. The second tuned cirtuned circuits areabove the signal frequency.

age at the ,means of the common ground connection and the couplingcondenser 7 connected between the intermediate tap 6 on coil 4 and theseries condenser 8. The intermediate tap 10 of coil 9 may be in turnconnected to the grid or inut terminal of a superheterodyne system ofwhich only the vacuum tube 12, which may be the first detector or radiofrequency amplifier,

is indicated. Tuning condensers 5 and 11 may have similar electricalcharacteristics and be arranged for uni-control, as indicated in thedrawing, as by mounting on the same shaft.

The antenna coil 3 is coupled mostly to the lower part of the coil 4,according to any satisfactory arrangement, manyof which are commonlyused. The two simultaneously tuned by means of the tuning condensers tothe sigwhich may be, for instance,

that is, 550 to 15.00 kilocycles. The superheterodyne system is usuallydesigned so that the image frequency lies above the signal frequency andmay fall within the range of 900 to 1850 kilocycles, in case theintermediate frequency is 17 5 kilocycles. vWhen the first tuned circuitis tuned as a whole to the signal frequency, the upper part of coil 4and the condenser 5 form a resonant rejector circuit between tap 6 andthe ground; The

, rejector circuit contains a smaller inductance of the entire tunedcircuit and is always resonsant to a frequency By proper location of thetap 6 on coil 4, the rejector circuit canv be made to tune overapproximately. the image frequency range. When the entire circuit'4, 5is tuned over the broadcast band with the tap 6 at such a point as togive about 45% of the'voltage existing across the entire coil ,4, therejector circuit will tune over a range offrom 750 to 2040 kilocycles.With a uniformly wound helical coil, 45% of the voltage-would .beobtained if the output included about 45% of the total number of turnsin the coil. It is to be noted that this gives approximately the imagefrequency than that therefore I range given above: The rejector circuit1s,

with a 45% tap, tuned exactly to the image I frequency of 1320kilocycles when the signal frequency is 970 kilocycles.

The rejector circuit arranged with the roper location of tap 6 thereforegreatly lncreases the attenuation of the .image frequency as-measured attap 6. It canvconsequently be seen that the voltage-gain characteristiccurve of the portion of the secondary 4 below the tap 6'will show zerovoltimage frequency, whereas the naturalresonance of the circuit may besuch that a considerable voltage will be developed at a frequency thesame amount on the other side of the signal frequency, thus producing anon-symmetrical curve relative to the voltages of the tapped portion ofthe coil 4. 'It is desirable to couple circuit 4, 5 and circuit 9, 11 byan amount somewhere near .the optimum value, which may be between 0.5%and 1%. This may be accomplished by making the capacity of .thecondenser 7 of the order of the minimum capacity of the circuit 9, 11and making the. capacity of the condenser 8 several times greater thanthe maximum of the capacity of the circuit 9, 11. There is no additionalgain when this coupling is greater than optimum. Therefore,

no loss of sensitivity results from coupling the upper end of coil 4.There is also the definite advantage of the greater imagefrequencyattenuation obtainable by taking the voltage The second circuit 9, 11 istuned to the signal frequency, and may or may not employ a tapconnection similar to tap 6 on coil 4. A similar tap 10 is shown in thediagram which would result in further increase in the attenuation of theimage frequency. It is to be noted that the presence or absence of tap10 does not afiect the advantage to be gained by use of tap 6. Tap 10has the disadvantage .of reducing the signal voltage output from circuit9, 11 although the imagefrequency-reduction is more than thesignalfrequency reduction.

It is convenient to refer to tap 6 as a-node point relative to groundfor theimage-frequency current since there is approximately from tap 6,as described above. 7

zero image-frequency voltage between this several useful and operativealternatives are known'in the art. The essential feature is that thesecond tuned circuit is coupled to the first by means responsive tosignal-frequency currents in the first tuned circuit and unresponsive toimage-frequency currents in the first tuned circuit. The preferredembodiment described herein-includes in such means, the tap 6 forattenuating imagefrequency currents and condensers 7 and 8 forconducting the signal-frequency currents.

What I claim is:

1. In a superheterodyne radio receiver, means for rejecting the imagefrequency, which comprise an input transformer, a tuned radio-frequencycircuit including the secondary of said transformer, a second tunedradio-frequency circuit, and means connecting said tuned radio-frequencycircuits, said last mentioned means including a connection to a portionof the first tuned circuit which the image frequency.

2. A radio-frequency tuning arrangement for a radio receiver, whichcomprises a cir cuit tuned to a current of the signal frequency, asecondcircuit tuned to the same frequency, a coupling circuit connectingsaid circuits, said coupling circuit being connected across a portion ofthe impedance of the first mentioned circuit, the terminals of whichportion are at node potential relative to current of an undesiredfrequency and across a portion of the impedance of the second mencurrentwith a first circuit upon tloned circuit.

3. In a superheterodyne recelver means for rejecting the image frequencywhich comprise a circuit resonant to the signal fre quency, a secondcircuit resonant to the signal frequency, circuits connected at pointsin the first of said circuits which are at node potential relative tocurrents of the image frequency and connected across a part of thecapacitive reactance of the second of said circuits, whereby the currentof the. image frequency is attenuated and the gain in amplification ofthe desired signal frequency current lost in said first mentionedcircuit is compensated for by gain in amplification of said current inthe second tuned circuit.

4. The combination of an electrical system responsive to a desiredfrequency and to an undesired frequency, which comprises a first whichare impressed signals of both of said frequencies, a second circuitconnected to said system, both of said circuits being individuallyresonant to currents of the desired frequency, said first circuitincluding two points which are node points for currents of the undesiredfrequency, and a coupling circuit connected to said two points andcoupled to said second circuit whereby sig nals having said undesiredfrequency are greatly attenuated.

5. Thecombination of an electrical system" responsive to desired andundesired frequency which are impressed currents of desired andundesired signal frequencies. a second circuit, said first and secondcircuits being individually resonant to currents of the desired signal,said first circuit having two points which are node points for currentsof the undesired frequency, and a coupling circuit connected to said twopoints and coupled to said second circuit whereby signalshaving saidundesired frequency are greatly attenuated, said coupling circuitproviding substantially optimum coupling between said first and secondcircuits, whereby the attenuation of currents of said desired frequencyis reduced to a minimum.

6. An electrical network adapted to select any desired frequency withina predetermined range and to simultaneously reject an undesiredfrequency which differs from said de- .being adapted to receive andmeans connecting said a radio responsive device and sired frequency by aconstant difference frequency, which comprises in combination an inputcircuit, an output circuit, and a couphng network, said input circuithavlng a variable tuning condenser and a fixed induc-.

tance, said inductance being divided in two parts by an intermediatetap, one of said parts induced voltages from a signal-receiving deviceand having its terminals connected to said coupling network, said outputcircuit having a variable tuning condenser and a fixed inductance, saidoutput circuit being coupled to said network and said circuits beingtuned to resonance at said desired frequency.

7. An electrical network adapted to select any desired frequency withina predetermined range and simultaneously to reject an undesiredfrequency which differs from said desired frequency by a constantdifference frequency, circuit, an output circuit, and a coupling networkincluding in series a fixed capacity'external pacity included in serieswith said output circuit, said input circuit having a variable tuningcondenser and a fixed inductance divided in two parts by an intermediatetap, one of said two parts being adapted to receiveinduced voltagesfrom,a signal receiving devicev comprlslng'in combination an input' toboth of said circuits and a fixed caa variable tuning condenser and afixed inductance and said circuits'being tuned to resonance at saiddesired frequency.

8. In a superheterodyne radio receiver means for rejecting the imagefrequency which comprises a circuit resonant to the signal frequency, aradio responsive device, and means connecting said radio responsivedevice to said circuit connected to points in said circuit which are atnode potential relative to currents of the image frequency.

9. In a superheterodyne receiver means for rejecting the image frequencywh ch comprises an input transformer, including the secondary of saidtransformer,

means connecting said ra'dio responsive device and sai connection to thesaid tuned circuit which is at node potential relative to currents ofthe image frequency.

10. In a superheterodyne radio receiver means or rejecting the undesiredimage frequency currents which comprise an input transformer, anoscillatory circuit including the secondary of said transformer, acondenser for tuning said circuit, a radio responsive frequency, saidpoints being so selected that.

tuned circuit, said means including a:

a tuned circuit I said tuning means will vary the frequency to whichsaid points are at node potential at the same time that it varies thetuning of the circuit to the desired signal, and the points will be atnode potential relative to the image.frequency at any desired point ofthe tuningra'ngeof said receiver.

11. In a sup-erheterodyne radio receiver means for rejecting theundesired image frequency currents which comprise an input transformer,an oscillatory circuit including the secondary of sa d transformer, acondenser for tuning said circuit, a second oscillatory circuit, acondenser for tuning said second oscillatory circuit and means forcoupling a said oscillatory circuits including connections to a portionof the first mentoned oscillatory circuit. which connections are at nodepotential relative to currents of the image frequency, said points beingso selected that the "tuning means of said circuit will vary thefrequency to which said connections are at node potential at the sametime that t varies the tuning of said circuit to the desired signal, andsaid points being so selected that the connections will to the imagefrequency at any desired point of the tuning range of said receiver.

12. In a superheterodyne radio receiver a circuit adapted to suppressthe image frequency which comprises a first tuned circuit, a variablecondenser for tuning said circuit to cause it to respond to thefrequency of the signal current, a second tuned circuit, a variablecondenser adapted to tune the second tuned circuit, to respond to thesignal frequency, a circuit connecting said tuned circuits connectedacross a portion of the inductance of the first of said tuned circuitswhich are at node potential relative to currents of the image frequencyand coupled to the second tuned circuit, whereby currents of the imagefrequency will be attenuated and the currents of said signal frequencywill be amplified in the second tuned circuit to compensate for theundesired attenuation of these signals in the first tuned circuit, aradio responsive device and a connection from said second tuned circuitto said radio responsive device connected to a point in the inductanceof the second tuned circuit which is at node potential relative tocurrents of the image frequency, whereby image frequency currents arefurther attenuated, said tuning condensers being so disposed in each ofsaid tuned circuits that they will s multaneously tune the frequencyrelative to which the selected points are atnode potential and thefrequency to which said circuits are responsive. f

In testimony whereof I affix my signature.

HAROLD A. WHEELER.

be at node potential relative

